Process of making white leather



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PROCESS OF MAKING WHITE LEATHER John Arthur Wilson, Buford, 6a., assignor to Hall Laboratories, Inc., Pittsburgh, Pa., a corporation of Pennsylvania No Drawing.

Application November 9, 1938,

Serial No. 239,679

5 Claims.

This invention relates to a process of making white washable leather which has superior properties, as compared with the best white leathers heretofore on the market.

White leather made according to prior processes has been made white by the use of white filling p'gments. This has been necessary, because of the fact that the leather itself did not have suflicient whiteness to be usedalone. These previously known white leathers were not white entirely through their thickness but only to a depth to which the white filling pigment had penetrated. As a result, upon repeated cleaning, the whiting material wore off and the natural color of the leather appeared.

I have discovered a process by which white leather may be made which is white entirely through its thickness and which does not require the use of white filling pigments. Thus the leather can be cleaned by wiping with a cloth dampened with soap and water or with naphtha or carbon tetrachloride or other cleaning agent and does not require the use of white shoe. polishes.

'In addition to its whiteness, the leather has certain very valuable physical and chemical properties which make its use advantageous and distinguish it from prior known white leather."

White calf leather made according to the process hereafter described in detail has a long silky fiber "and a tensile strength of at least 3900 lbs. per scguareinch. It has a tearing resistance of at least 6 lbs. and relative porosity of at least 1,000. It can be stretched at least 40% before the grain cracks and has a water absorption when immersed in water at F. for 30 minutes of not over 125%. l

In the following table are given various physical and chemical properties of various white calf leathers. Sample A is one of the best white calf leathers on the market in which the whiteness was produced by filling with titanium oxide. Samples B. C and D are three white calf leathers made according to my preferred process:

Table A B C D Ten. str ..l .1b./su.in 3356 i268 4743 3914 Tearing resistance ..pounds 4. 8 6. 3 7. 7 7. 5 Stretch when grain cracked percent" 7 34 40 45 43 Bel. porosity 0 F D 375 1091 1000 1500 Oat tinat7 min. B, bqorp 0 percent" 134-. 115 1 87.4 124.7 Combined P10 hide substance percent u. 00 1 2. 45 2. 16

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The methods used in measuring the physical properties of the leather are to be found in the book Analysis of Leather, by John Arthur Wilson and Henry Baldwin Merrill, McGraw-Hill Book Co., New York.

In leather for certain uses-for example, white calf and other shoe upper leathers, it is desirable that the leather be porous, so as to allow free circulation of air, provided that the leather has suflicient tensile strength, tearing resistance and wear resistance. It is also desirable that the amount of water absorption be not too great, as otherwise the leather may become too wet in cleaning or in use, when exposed to water. It

will be noted that my leather has a combination leather in accordance with the present inven-' tion is as follows:

Bleaching The bleaching operation has been found to improve the appearance of the grain; particularly for full grain leather, by freeng the grain from impurities that would otherwise discolor it.

The quantities given below are per onejhundredj oearcn nuum I pounds weight of calf skins containing 23% of A actual hide substance, For other conditions of.

The stock is taken directly from the bate and the quantities given. below are per lb. bated weight. Put pack into drum; start running and add 7.5 lb.. salt and 1 lb. sulfuric acid in 10 gal. water at 60 F. Run 10 minutes and add 0.5 lb';

50 F. Run 20 minutes and add 0.75 anhydrousso potassium permanganate in 3 gaLwaterat 60 dium bisulfite in 2 gal. water at 60 Run 30 minutes longer, when stock should appear white and the pH value of the liquor should be about 4.0. Add 1 lb. sodium,.;bicarboz'iate in "2.5 gel.

water at 60 F. and run 1 hour, when the pH value of the liquor should lie between 6.0 and 7.0. If it is lower than 6.0, add enough more bicarbonate to raise it to 7.0. Run 1 hour longer and then wash the stock in running water at 60 F. for minutes.

The stock is then given aformalin pretanning treatment.

Formalz'n pretanning This operation is used chiefly for white leather, in order to make it fuller and softer. The quantlties given below are per one hundred pounds bated weight. Put pack into drum, start running and add 4 lb. formalin solution of formaldehyde) and 0.4 oz. sulfuric acid in 8 gal. water at F. Run 2 hours, when tne pH value should lie between 5.5 and. 6.5 and should be adjusted to this range,.if necessary. Add 4 lb. sodium bicarbonate in 6 gal. water at 60 F. slowly, over a period or 15 minutes. Run 30 minutes longer, when the pH value of the liquor should be about 8.5; if below 8.5, add enough more bicarbonate to bring it to this value. Run 90 minutes longer, drain and wash in running water at 60 F. for 30 minutes. the temperature of the liquor to rise above 90 F.

For very light stock, the running times may be correspondingly shortened.

The formalin pretanning treatment is followed by a tannage with sodium metaphosphate sometimes referred to as Graham's salt. Graham-s salt, which consists principally of hexametaphosphate, is a glassy material which is assumed to be a complex of the general formula Na2(Na4PsO1a) although some authorities believe that salts of the formula Na5(NaPsO1s) and NadNazPsOm) may also be present.

' Sodium metaphosp ate tanning Put pack into drum, start running and add 3 lb. Grahams salt, 2.5 lb. sulphonated cocoanut oil and 1.25 lb. phosphated cocoanut oil in 10 gal. water at 60 F. Run 15 minutes andadd slowly, over a period of 30 minutes, 1.5 lb. sulfuric acid in 2 gal. water. Run 15 minutes and measure the pH value of the liquor. If it is above 2.2, add enough more sulfuric acid to lower it to 2.2. The pH value should be kept between 2.0 and 2.4 during the entire period of the tannage. Be careful not to let the temperature rise above F. If the temperature of the liquor rises above this point, stop the drum, open the door and allow to cool. Run until the stock is completely tanned.

The leather may be tested for completeness of tannage by cutting 011 pieces and soaking them in several changes of water. If fully tanned, they will not swell but will remain soft and flaccid. If the tannage is not complete, the untanned middle layer looks more translucent than the outer tanned layers, which appear white and opaque. This effect can be still more exaggerated by soaking a cutting in a solution of sulfuric acid of pH=2.2. A fully tanned piece of leather will not -swellin an acid solution of pH=2.2, whereas the untanned hide will.

Another method, particularly useful for thin stock where it is not easy to see a very thin, translucent layer, is to place a drop of pH indicator on a freshly-cut edge and note the uniformity of color throughout the entire thickness of the stock. If this color shows a pH value below 2.5 uniformly through the thickness of a cutting from the heaviest portion of the stock, the stock may be considered as fully tanned.

Do not allow The total tanning time required for sheepskins 'is about 2 hours; for kidskins about 3.5 hours; for calf, kip, and light sides, about 5 hours and for heavy steer hides, up to 24 hours.

Alum retanm'ng The stock for this retannage is taken immediately after the metaphosphate tanning. The quantities given below are per 100 lb. bated weight of stock. Put. pack into drum and wash in running water, at 60 F. for from 30 to 60 minutes, depending upon the thickness of the hides or skins. Drain and add 12 lbs. aluminum sulfate and 3 lb. salt in 12 gal. water at 60 F. Run

2 hours and then add 4 lb. soda ash in 4 gal. 1

water at 60 F. slowly, over a period of 45 minutes. Run30 minutes longer, when the pH value of the liquor shouldlie between 4.0 and 4.1. If the pH value is below this range, add enough more soda ash to bring it to 4.1. Run minutes longer and then horse the stock to drain, set out, and hang For goatskins, the hide-substance content of O bated goatskins is taken as 20% in these methods. Make adjustments, if it differs much from 20%. Follow the procedure for calf exactly, except for the following changes. In the formalin pretannage, use only 1.5 lbs. formalin instead of 4 lbs. and decrease the running time from 2 hours to 90 minutes. In the metaphosphate tanning, decrease the amount of metaphosphate from 3 lbs. to 2110s., the sulphonated cocoanut oil from 2.5 lbs. to 18 oz. and the phosphorated cocoanut oil from 1.25 lbs. to 9 oz. It will be found that the time required f9r complete tannage will be from one to two hours less than for calf.

For sheep, since sheepskins are generally purchased after dewooling and pickling, no bated weight is available. It is customary to decrease and press the stock before tanning. In these methods, the hide-substance content of the pressed weight is taken as 20% and adjustments should be made for known deviations from this. Proceed exactly as for goatskins, but use quantities given as per lbs. pressed weight instead of as per 100 lbs. bated weight. Omit the operation of formalin pretanning entirely. After hanging to dry, instead of dampening and staking,

proceed as for garment sheep or other type for which leather is being. produced.

Although I have specifically described my preferred process, it will be understood that the invention is not limited to the specific materials employed, nor to the precise quantities mentioned,

but that the invention may be otherwise embodied or practiced within the scope of the following claims.

ULLIU IIIU u U 'Ll u, I Lulu TREATMENT & CHEMICAL MODYIFL v CATTON OF TEXTILES & FIBERS,

with a solution of an alkali metal'metaphosphate,

and then with an alum' tanning solution.

3. The process of making white leather from. animal skin, which comprises bleaching the skin in a permanganate bleaching solution, treating the skini with aformaldehyde solution, then with a solution ofan alkali metal metaphosphate. and thereafter with an alum tanning; solution.

4. The process of makingwhite leather from animal skin, which comprises treating the skin with a. formaldehyde solution, thereafter with, an. alkali metal metaphos'phate solution maintained,

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5. The process of making white leather from animal skin, which comprisesbleaching the skin, treating it first with an acidformaldehyde solution and; then with an alkaline formaldehyde solution, thereafter treating it withv an alkali metal metaphosphate solution, maintained at a pH be-,

tween. about 2.0 and- 2.4-, and thereafter with an alum tanning solution.

J ARTHUR, WILSON. 

